279 research outputs found
A Modified Magnitude System that Produces Well-Behaved Magnitudes, Colors, and Errors Even for Low Signal-to-Noise Ratio Measurements
We describe a modification of the usual definition of astronomical
magnitudes, replacing the usual logarithm with an inverse hyperbolic sine
function; we call these modified magnitudes `asinh magnitudes'. For objects
detected at signal-to-noise ratios of greater than about five, our modified
definition is essentially identical to the traditional one; for fainter objects
(including those with a formally negative flux) our definition is well behaved,
tending to a definite value with finite errors as the flux goes to zero.
This new definition is especially useful when considering the colors of faint
objects, as the difference of two `asinh' magnitudes measures the usual flux
ratio for bright objects, while avoiding the problems caused by dividing two
very uncertain values for faint objects.
The Sloan Digital Sky Survey (SDSS) data products will use this scheme to
express all magnitudes in their catalogs.Comment: 11 pages, including 3 postscript figures. Submitted to A
Zero-Emission Vessels 2030: How do we get there?
Fossil fuels provide society in general,
as well as shipping, with a high-density
and low-cost energy source that is
comparatively easy to store, handle
and transport. We have had decades to
optimise the design, maintenance and
operation of the shipping system to suit
the fossil âparadigmâ. But the world is
changing. It is, therefore, unsurprising
that when looking for a non-fossil,
zero-emission and sustainable energy
source, as we must urgently now do, itâs
difficult to see an obvious âsilver bulletâ
PopFor : A new model for estimating poplar yields
Yield and soil data for this project has been supplied by Rainer Schlepphorst, Holger Hartmann and Dieter Murach from HNEE, Germany, from the BIODEM project. Soil water and groundwater data were supplied by Markus Schmidt, HNEE, Germany. We would like to thank Shell and the University of Aberdeen CLSM for funding this work with a studentship. The MiscanFor modelling was supported by UK NERC ADVENT (NE/1806209) and FAB-GGR (NE/P019951/1) project funding.Peer reviewedPostprin
SDSS Pre-Burst Observations of Recent Gamma-Ray Burst Fields
In this paper, we present Sloan Digital Sky Survey (SDSS) photometry and
spectroscopy in the fields of 24 gamma-ray bursts (GRBs) observed by Swift,
including bursts localized by Swift, HETE-2, and INTEGRAL, after December 2004.
After this bulk release, we plan to provide individual releases of similar data
shortly after the localization of future bursts falling in the SDSS survey
area. These data provide a solid basis for the astrometric and photometric
calibration of follow-up afterglow searches and monitoring. Furthermore, the
images provided with this release will allow observers to find transient
objects up to a magnitude fainter than possible with Digitized Sky Survey image
comparisons.Comment: Submitted in PASP. Data for GRB fields included in this release can
be found at http://mizar.as.arizona.edu/grb/public. Updated with corrected
object counts. Replaced with revised versio
Spectroscopic Target Selection in the Sloan Digital Sky Survey: The Quasar Sample
We describe the algorithm for selecting quasar candidates for optical
spectroscopy in the Sloan Digital Sky Survey. Quasar candidates are selected
via their non-stellar colors in "ugriz" broad-band photometry, and by matching
unresolved sources to the FIRST radio catalogs. The automated algorithm is
sensitive to quasars at all redshifts lower than z=5.8. Extended sources are
also targeted as low-redshift quasar candidates in order to investigate the
evolution of Active Galactic Nuclei (AGN) at the faint end of the luminosity
function. Nearly 95% of previously known quasars are recovered (based on 1540
quasars in 446 square degrees). The overall completeness, estimated from
simulated quasars, is expected to be over 90%, whereas the overall efficiency
(quasars:quasar candidates) is better than 65%. The selection algorithm targets
ultraviolet excess quasars to i^*=19.1 and higher-redshift (z>3) quasars to
i^*=20.2, yielding approximately 18 candidates per square degree. In addition
to selecting ``normal'' quasars, the design of the algorithm makes it sensitive
to atypical AGN such as Broad Absorption Line quasars and heavily reddened
quasars.Comment: 62 pages, 15 figures (8 color), 8 tables. Accepted by AJ. For a
version with higher quality color figures, see
http://archive.stsci.edu/sdss/quasartarget/RichardsGT_qsotarget.preprint.p
Effect of early vasopressin vs norepinephrine on kidney failure in patients with septic shock. The VANISH Randomized Clinical Trial
IMPORTANCE: Norepinephrine is currently recommended as the first-line vasopressor in septic shock; however, early vasopressin use has been proposed as an alternative. OBJECTIVE: To compare the effect of early vasopressin vs norepinephrine on kidney failure in patients with septic shock. DESIGN, SETTING, AND PARTICIPANTS: A factorial (2Ă2), double-blind, randomized clinical trial conducted in 18 general adult intensive care units in the United Kingdom between February 2013 and May 2015, enrolling adult patients who had septic shock requiring vasopressors despite fluid resuscitation within a maximum of 6 hours after the onset of shock. INTERVENTIONS: Patients were randomly allocated to vasopressin (titrated up to 0.06 U/min) and hydrocortisone (nâ=â101), vasopressin and placebo (nâ=â104), norepinephrine and hydrocortisone (nâ=â101), or norepinephrine and placebo (nâ=â103). MAIN OUTCOMES AND MEASURES: The primary outcome was kidney failure-free days during the 28-day period after randomization, measured as (1) the proportion of patients who never developed kidney failure and (2) median number of days alive and free of kidney failure for patients who did not survive, who experienced kidney failure, or both. Rates of renal replacement therapy, mortality, and serious adverse events were secondary outcomes. RESULTS: A total of 409 patients (median age, 66 years; men, 58.2%) were included in the study, with a median time to study drug administration of 3.5 hours after diagnosis of shock. The number of survivors who never developed kidney failure was 94 of 165 patients (57.0%) in the vasopressin group and 93 of 157 patients (59.2%) in the norepinephrine group (difference, -2.3% [95% CI, -13.0% to 8.5%]). The median number of kidney failure-free days for patients who did not survive, who experienced kidney failure, or both was 9 days (interquartile range [IQR], 1 to -24) in the vasopressin group and 13 days (IQR, 1 to -25) in the norepinephrine group (difference, -4 days [95% CI, -11 to 5]). There was less use of renal replacement therapy in the vasopressin group than in the norepinephrine group (25.4% for vasopressin vs 35.3% for norepinephrine; difference, -9.9% [95% CI, -19.3% to -0.6%]). There was no significant difference in mortality rates between groups. In total, 22 of 205 patients (10.7%) had a serious adverse event in the vasopressin group vs 17 of 204 patients (8.3%) in the norepinephrine group (difference, 2.5% [95% CI, -3.3% to 8.2%]). CONCLUSIONS AND RELEVANCE: Among adults with septic shock, the early use of vasopressin compared with norepinephrine did not improve the number of kidney failure-free days. Although these findings do not support the use of vasopressin to replace norepinephrine as initial treatment in this situation, the confidence interval included a potential clinically important benefit for vasopressin, and larger trials may be warranted to assess this further. TRIAL REGISTRATION: clinicaltrials.gov Identifier: ISRCTN 20769191
An Erupting Classical Nova in a Globular Cluster of M87
Only one certain classical nova eruption has ever been detected inside a
globular cluster - nova 1860 A.D. (T Sco) in M80. During a survey of M87 we
have detected an erupting star coincident (to within 0.08 pixels) with a
globular cluster of that giant elliptical galaxy. We are able to discount
variables in the foreground or background of M87. The light curve and color of
the erupting star match those expected for a nova at the distance of M87. The
chance superposition of an M87 field nova on the globular cluster is very
unlikely but cannot be completely ruled out.Our detection hints at a globular
cluster nova frequency novae/cluster/year, much higher than
previous observations have suggested
Computational modelling of NF-ÎșB activation by IL-1RI and its co-receptor TILRR, predicts a role for Cytoskeletal Sequestration of IÎșBα in inflammatory signalling.
The transcription factor NF-ÎșB (nuclear factor kappa B) is activated by Toll-like receptors and controlled by mechanotransduction and changes in the cytoskeleton. In this study we combine 3-D predictive protein modelling and in vitro experiments with in silico simulations to determine the role of the cytoskeleton in regulation of NF-ÎșB. Simulations used a comprehensive agent-based model of the NF-ÎșB pathway, which includes the type 1 IL-1 receptor (IL-1R1) complex and signalling intermediates, as well as cytoskeletal components. Agent based modelling relies on in silico reproductions of systems through the interactions of its components, and provides a reliable tool in investigations of biological processes, which require spatial considerations and involve complex formation and translocation of regulatory components. We show that our model faithfully reproduces the multiple steps comprising the NF-ÎșB pathway, and provides a framework from which we can explore novel aspects of the system. The analysis, using 3-D predictive protein modelling and in vitro assays, demonstrated that the NF-ÎșB inhibitor, IÎșBα is sequestered to the actin/spectrin complex within the cytoskeleton of the resting cell, and released during IL-1 stimulation, through a process controlled by the IL-1RI co-receptor TILRR (Toll-like and IL-1 receptor regulator). In silico simulations using the agent-based model predict that the cytoskeletal pool of IÎșBα is released to adjust signal amplification in relation to input levels. The results suggest that the process provides a mechanism for signal calibration and enables efficient, activation-sensitive regulation of NF-ÎșB and inflammatory responses
Photometric Calibration of the Swift Ultraviolet/Optical Telescope
We present the photometric calibration of the Swift UltraViolet/Optical
Telescope (UVOT) which includes: optimum photometric and background apertures,
effective area curves, colour transformations, conversion factors for count
rates to flux, and the photometric zero points (which are accurate to better
than 4 per cent) for each of the seven UVOT broadband filters. The calibration
was performed with observations of standard stars and standard star fields that
represent a wide range of spectral star types. The calibration results include
the position dependent uniformity, and instrument response over the 1600-8000A
operational range. Because the UVOT is a photon counting instrument, we also
discuss the effect of coincidence loss on the calibration results. We provide
practical guidelines for using the calibration in UVOT data analysis. The
results presented here supersede previous calibration results.Comment: Minor improvements after referees report. Accepted for publication in
MNRA
High resolution spatial modelling of greenhouse gas emissions from land use change to energy crops in the UK
We implemented a spatial application of a previously evaluated model of soil GHG emissions, ECOSSE, in the United Kingdom to examine the impacts to 2050 of land-use transitions from existing land use, rotational cropland, permanent grassland or woodland, to six bioenergy crops; three âfirst-generationâ energy crops: oilseed rape, wheat and sugar beet, and three âsecond-generationâ energy crops: Miscanthus, short rotation coppice willow (SRC) and short rotation forestry poplar (SRF). Conversion of rotational crops to Miscanthus, SRC and SRF and conversion of permanent grass to SRF show beneficial changes in soil GHG balance over a significant area. Conversion of permanent grass to Miscanthus, permanent grass to SRF and forest to SRF shows detrimental changes in soil GHG balance over a significant area. Conversion of permanent grass to wheat, oilseed rape, sugar beet and SRC and all conversions from forest show large detrimental changes in soil GHG balance over most of the United Kingdom, largely due to moving from uncultivated soil to regular cultivation. Differences in net GHG emissions between climate scenarios to 2050 were not significant. Overall, SRF offers the greatest beneficial impact on soil GHG balance. These results provide one criterion for selection of bioenergy crops and do not consider GHG emission increases/decreases resulting from displaced food production, bio-physical factors (e.g. the energy density of the crop) and socio-economic factors (e.g. expenditure on harvesting equipment). Given that the soil GHG balance is dominated by change in soil organic carbon (SOC) with the difference among Miscanthus, SRC and SRF largely determined by yield, a target for management of perennial energy crops is to achieve the best possible yield using the most appropriate energy crop and cultivar for the local situation
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